The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

Edexcel C2 Exam question...

I was recently looking over the 2014 June exam and noticed it said this for one of the sin, tan question.

Solve, for -pi to pi, the equation2tanx – 3sinx = 0

"Solutions based entirely on graphical or numerical methods are not acceptable".

I'm used to using the CAST diagram for such questions. Does this mean that i can't use it or does it mean something else?

Scroll to see replies

Original post by beast709
I was recently looking over the 2014 June exam and noticed it said this for one of the sin, tan question.

Solve, for -pi to pi, the equation2tanx – 3sinx = 0

"Solutions based entirely on graphical or numerical methods are not acceptable".

I'm used to using the CAST diagram for such questions. Does this mean that i can't use it or does it mean something else?


Key word is 'entirely'. Thus you can use it, supposing your answer employs the use of algebra and the trig identity rules.
I think it's so you don't use a numerical method of intersections. This is where you would draw 2tanx an 3sinx and see where they cross over (2tanx = 3sinx at these points). I would think you can use identities and CAST, as High Stakes says too :smile:
Reply 3
Avatar for beast709
beast709
OP
2
Original post by High Stakes
Key word is 'entirely'. Thus you can use it, supposing your answer employs the use of algebra and the trig identity rules.


Yeah that makes sense. Thanks!
Wait up

How would you even solve that equation :hmmm:

Posted from TSR Mobile
Original post by beast709
I was recently looking over the 2014 June exam and noticed it said this for one of the sin, tan question.

Solve, for -pi to pi, the equation2tanx – 3sinx = 0

"Solutions based entirely on graphical or numerical methods are not acceptable".

I'm used to using the CAST diagram for such questions. Does this mean that i can't use it or does it mean something else?


They don't want you to use iteration or Newton-Raphson method etc. to solve the equation. The also don't want you to draw the graphs of each function(2tan x and 3sin x) and solve it that way.

Doing some algebra and finding a solution and finding the others via CAST is fine.
What have you tried?
Original post by morgan8002
They don't want you to use iteration or Newton-Raphson method etc. to solve the equation. The also don't want you to draw the graphs of each function(2tan x and 3sin x) and solve it that way.

Doing some algebra and finding a solution and finding the others via CAST is fine.


They also don't want people just typing it into a calculator and pressing solve

Posted from TSR Mobile
2(sinx/cosx) -3sinx =0

What next :hmmm:

Posted from TSR Mobile
Original post by Straight Quant.
2(sinx/cosx) -3sinx =0

What next :hmmm:

Posted from TSR Mobile


Give them a common denominator then subtract

Posted from TSR Mobile
Original post by Straight Quant.
2(sinx/cosx) -3sinx =0

What next :hmmm:

Posted from TSR Mobile


Naaah i got this fam i think

Divide through by sin x innit?

Posted from TSR Mobile
Original post by Straight Quant.
2(sinx/cosx) -3sinx =0

What next :hmmm:

Posted from TSR Mobile


Are you saying 'what next' as in, I did it. Or do you want help (because you're yet to complete it).
I remember last summer when I done the actual c2 exam found that question, so easy, now even though I do A2 no idea how you solve it LOL
Original post by Straight Quant.
Naaah i got this fam i think

Divide through by sin x innit?

Posted from TSR Mobile


What do you mean by that? Give it a try.
Original post by High Stakes
What do you mean by that? Give it a try.


Divide everything by sinx?

Then you'll have 2/(cosx) -3 = 0

Then you can just rearrange and solve, no?

Posted from TSR Mobile
Original post by High Stakes
What do you mean by that? Give it a try.


You will eliminate at least one solution by doing that

Posted from TSR Mobile
Original post by samb1234
Give them a common denominator then subtract

Posted from TSR Mobile


Bur you cant get a common denominator :hmmm:

If i were to multiply -3sinx by 1/cosx, i would have to multiply sinx/cosx by 1/cosx as well

Posted from TSR Mobile
Original post by Straight Quant.
Bur you cant get a common denominator :hmmm:

If i were to multiply -3sinx by 1/cosx, i would have to multiply sinx/cosx by 1/cosx as well

Posted from TSR Mobile


Multiply -3sinx by cos/cos

Posted from TSR Mobile
Original post by samb1234
Multiply -3sinx by cos/cos

Posted from TSR Mobile


Still dont work

If i do that, wouldnt i have to multiply 2sinx/cosx by cosx/cosx, giving me cos^(2)x in the denominator

**** this question

Posted from TSR Mobile
Original post by samb1234
They also don't want people just typing it into a calculator and pressing solve

Posted from TSR Mobile

True. I don't know exactly what methods they use but they are similar.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you